Screw-rotor machine for compressible fluids

ABSTRACT

A SCREW-ROTOR MACHINE FOR COMPRESSIBLE FLUIDS, WHEREIN THE PROFILE OF THE HEAD OF EACH OF THE DRIVING ROTOR LOBES IS DEFINED BY TWO LENGTHS OF EPICYCLOIDS INTERCONNECTED BY A CONJUGATE CURVE. THE CONJUGATED CURVE IS A LENGTH OF THE ELONGATED HYPOCYLOID FORMED DURING ROLLING OF A BASE CIRCLE ALONG THE INNER SIDE OF DRIVING ROTOR ROLLING CIRCLE BY A POINT LOCATED OUTSIDE THE BASE CIRCLE WHOSE RADIUS IS LARGER THAN ZERO BUT SMALLER THAN THE RADIUS OF THE ROLLING CIRCLE.

May 30, 1972 P. E AMOSOV FFAL 3,666,384

SCREW-ROTOR MACHINE FOR COMPRESSIBLE FLUIDS Filed Oct 20, 1970 United States Patent Office- 3,666,384 SCREW-ROTOR MAgl LllNE FOR COMPRESSIBLE UIDS Pavel Evgenievieh Amosov, Kronverkskaya ulitsa 29/37,

kv. 87; Leonid Mikhailovich Imyanitov, 6-ya Sovetskaya ulitsa 33, kv. 4; Vitaly Konstantinovich Smekhov, Ulitsa Kolomenskaya 33/40, kv. 25; and Valery Leonidovich Trofimov, Ulitsa Matrosova 12, kv. 8, all of Leningrad, U.S.S.R.

Filed Oct. 20, 1970, Ser. No. 82,297 Int. Cl. F01c 1/16, 1/24; F04c 1/10 US. Cl. 418-201 1 Claim ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to devices for compressing compressible fluids or for converting the energy of a compressed fluid into a mechanical energy and, more specifically, to screw-rotor machines for compressible fluids.

Known in the art is a screw-rotor machine for compressible fluids comprising a driving rotor and a driven rotor, both installed in a casing and coacting with each other and with the casing.

The profile of the lobe head of the driving rotor is constituted in the face section by two lengths of epicycloids interconnected by a curve which is the arc of a circle whose center lies on the rolling circle of the driving rotor.

The profile of the lobe base of the driven rotor follows the profile of the lobe head of the driving rotor.

Gas is compressed in the machine owing to a reduction in the volume of the spaces separated from the suction pipe. These spaces are confined by the surfaces of the driving and driven rotors, on the one hand, and the casing surface on the other, with the latter being essentially the surface of two straight intersecting cylinders with parallel axes.

In order to seal off the spaces of the rotors during the periods of the fluid suction and discharge, it is necessary that the surfaces of the rotors and those of the casing should contact each other and that their common line of contact should be uninterrupted.

In the known machine, the lines of contact between the rotors and between the rotors and the casing are uninterrupted, provided they are taken separately.

A disadvantage of the known rotor machine lies in the break in the common line of contact, with the break occurring where the contact line between the rotors joins the contact line between the rotors and the casing. The break in the common line of contact is caused by deviation of the rotor lobe engagement from the pointtype epicycloidal engagement which results in the formation of a three-dimensional channel communicating the rotor spaces with each other and with the discharge pipe of the machine during the gas compression period, and in the axial leakage of the screw-rotor machine.

Another disadvantage of the known screw-rotor machine is its low volumetric coefiicient which is defined as a ratio 3,666,384. Patented May 30, 1972 of the machine output per revolution of the driving rotor to the volume of the casing recess. In the known machine, this volumetric coefiicient does not exceed 30% which is attributable to an unfavorable relation (-05) between the height of the head of the driving rotor lobe and its thickness measured along the arc of the driving rotor rolling circle.

The above disadvantages lead to power losses and impair the weight and dimensional characteristics of the machine.

An object of the present invention is to provide a screwrotor machine with such a shape of the profile of the driving rotor lobe head as to reduce the axial leakage in the machine and increase its volumetric coetficient.

SUMMARY OF THE INVENTION This object is accomplished by providing a screwrotor machine for compressible fluids in which, according to the invention, the conjugate curve of the profile is a length of an elongated hypocycloid generated during rolling of a base circle over the inner side of the driving rotor rolling circle by the point located outside the base circle whose radius is larger than zero but smaller than the radius of the driving rotor rolling circle.

BRIEF DESCRIPTION OF THE DRAWINGS Now the invention will be made more apparent by way of example with reference to the appended drawing in which the sole view is a cross section of the screwrotor machine for compressible fluids according to the invention.

DETAILED DESCRIPTION OF THE INVENTION The screw-rotor machine comprises a driving rotor 2 and a driven rotor 3 installed in a casing 1. Lobes 4 of the driving rotor 2 consist mainly of heads, only, while lobes 5 of the driven rotor 3 consist mainly of only lobe bases. The number of lobes 4 of the driving rotor 2 should not be less than two, whereas the number of lobes 5 of the driven rotor 3 should not be less than three.

The profile of the head of the lobe 4 is formed in the face section by two lengths A C of epicycloids interconnected by a conjugate curve which is a section of an elongated hypocycloid C,D,C

The head of the lobe 4 is symmetrical relative to a radical line drawn to head D of the lobe 4. The epicycloids A C are formed when a base circle 6 of the rotor 3 rolls over the outer side of a rolling circle 7 of the driving rotor 2. Points A on which the epicycloids are based are located on the base circle 6. Starting points A, of the epicycloids are located on the rolling circle 7 of the rotor 2.

The length of the elongated hypocycloid C D C is formed by a point S when base circle 8 of the rotor 2 rolls over the inner side of the rolling circle 7 of the driving rotor 2, with the point S being located at a distance from center 0 of the circle 8, which is equal to the height of the head of the lobe 4 plus the radius of the base circle 8.

During operation of the screw rotor machine, the fluid filling the spaces confined by the surfaces of the driving rotor 2, driven rotor 3, and the surface of the casing 1 changes its volume during rotation of the said rotors and moves from the inlet pipe of the machine to its outlet pipe (not shown).

In the screw-rotor machine according to the present invention in which the profile of the lobe head of the driving rotor is constituted by a length of an elongated hypocycloid smoothly joining the lengths of epicycloids, the relative thickness of the tooth is reduced, with the thickness being defined as the relation of the lobe width measured along the arc of the driving rotor rolling circle to the height of the lobe head.

Besides, the interruption of the summary line of contact, occurring while the continuous line of rotor contact joins the line of contact between the rotor and the casing is reduced; likewise, the relative line of contact is also reduced, with the relative line of contact being defined as the relation between the length of contact of the space to the cube root of its maximum volume.

The reduction of the relative thickness of the lobe increases the volume efficiency of the machine since the quantity of the fluid passing through the inlet and discharge pipes of the machine per revolution of the driving rotor is increased, with the rotor dimensions being unchanged.

The reduced interruption in the summary line of contact decreases the fluid leaks between the spaces whose volume is being reduced or increased, which steps up the economy of compression (or expansion) of the fluid, thus bringing this process considerably closer to the adiabatic one.

The reduction of the relative length of the contact line between the rotors reduces the amount of the fluid leaking inside the machine between the spaces whose volume is being reduced at one side and increased at the other.

This improves the economy of the process of compression (or expansion) and increases the amount of the fluid passing through the inlet and discharge pipes of the machine within one revolution of the driving rotor.

It should be pointed out that the profile of a lobe is understood as a line along which the surface of the lobe intersects the plane perpendicular to the axis of rotation of the rotor. The head of a lobe is a part of the lobe profile located beyond the limits of the rolling circle 7 of the driving rotor 2.

What we claim is:

1. A screw-rotor machine for compressible fluids comprising a casing; a driving rotor installed in said casing; said driving rotor having a base circle and a rolling circle; a driven rotor installed in said casing and coacting with said driving rotor; said driving rotor having lobes with profiled heads, the profiled heads being defined by two lengths of epicycloids interconnected by a conjugate curve which is a length of an elongated hypocycloid provided when the base circle of the driving rotor rolls along the inner side of the rolling circle of said driving rotor by a point located outside said base circle whose radius is larger than zero but smaller than the radius of said rolling circle of the driving rotor.

References Cited UNITED STATES PATENTS 11/1949 Whitfield 41820l 4/1967 Lysholm 418-201 X 

